1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to semiconductor chip packages utilizing stiffener frames and methods of making the same.
2. Description of the Related Art
Many current integrated circuits are formed as multiple dice on a common silicon wafer. After the basic process steps to form the circuits on the dice are complete, the individual dice are cut or singulated from the wafer. The singulated dice are then usually mounted to structures, such as circuit boards, or packaged in some form of enclosure.
One frequently-used package consists of a substrate upon which a die is mounted. The upper surface of the substrate includes electrical interconnects. The die is manufactured with a plurality of bond pads. A collection of solder bumps are provided between the bond pads of the die and substrate interconnects to establish ohmic contact. An underfill material is deposited between the die and the substrate to act as a material that prevents damage to the solder bumps due to mismatches in the coefficients of thermal expansion between the die and the substrate, and an adhesive to hold the die. The substrate interconnects include an array of solder pads that are arranged to line up with the die solder bumps. After the die is seated on the substrate, a reflow process is performed to enable the solder bumps of the die to metallurgically link to the solder pads of the substrate. After the die is mounted to the substrate, a lid is attached to the substrate to cover the die. Some conventional integrated circuits, such as microprocessors, generate sizeable quantities of heat that must be ferried away to avoid device shutdown or damage. For these devices, the lid serves as both a protective cover and a heat transfer pathway.
One conventional type of substrate consists of a core laminated between upper and lower build-up layers. The core itself usually consists of four layers of glass filled epoxy. The build-up layers, which may number four or more on opposite sides of the core, are formed from some type of resin. Various metallization structures are interspersed in the core and build-up layers in order to provide electrical pathways between pins or pads on the lowermost layer of the substrate and pads that bond with the chip solder bumps.
The core provides a certain stiffness to the substrate. Even with that provided stiffness, conventional substrates still tend to warp due to mismatches in coefficients of thermal expansion for the chip, underfill and substrate. However, there is a need to provide shorter electrical pathways in package substrates in order to lower power supply inductance and improve power fidelity for power transferred through the substrate. The difficult problem is how to reduce the electrical pathways without inducing potentially damaging substrate warping.
One conventional technique for addressing package substrate warpage involves the use of a stiffener ring on the die side of the package substrate and a lid attached to the stiffener ring, typically by glue of some sort. Some conventional stiffener rings are made of metallic materials, while others are formed from plastics. Regardless of composition, a typical conventional stiffener ring frames the die and has a flat outer surface that is vertically aligned with a corresponding flat outer surface of the lid. When the lid is secured to the stiffener frame, the glue is squeezed and may bleed out laterally, much like peanut butter from the edges of a sandwich. Even after curing, particles of the glue may sprinkle down on sensitive electronic structures, such as tiny socket structures, and cause electrical problems.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.